Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$50.71	7.339%	$54.4316	$54.43	$54.45	$54.40
Purchase #2	$157.81	5.170%	$165.9688	$165.97	$165.95	$166.00
Purchase #3	$18.74	12.841%	$21.1464	$21.15	$21.15	$21.10
Purchase #4	$85.45	4.605%	$89.385	$89.39	$89.40	$89.40
Purchase #5	$142.60	7.556%	$153.3749	$153.37	$153.35	$153.40
Purchase #6	$182.94	5.779%	$193.5121	$193.51	$193.50	$193.50
Purchase #7	$191.87	11.417%	$213.7758	$213.78	$213.80	$213.80
7 purchase totals =	$830.12		$891.5946	$891.60	$891.60	$891.60